1. Field of the Invention
This invention relates to a method of draw forming a desired contour along outer diameter of a tubular workpiece, and more particularly, to such a method for controlling and minimizing an unwanted increase to the wall thickness along the altered contours of the tubular workpiece useful particularly to form a tubular metal workpiece having contours to meeting stringent shape and wall thickness requirements.
2. The Prior Art
The metal working operations of the present invention alter the surface contour of a tube comprised of ferrous or non-ferrous metal and the form of any of diverse cross sectional configurations, including rounds, squares and rectangles. The metal working operations are particularly useful to provide workpieces for the manufacture of automotive fuel tank filler tube or an automotive instrument panel support beam. The methods of manufacturing contoured workpiece used for the manufacture of an automotive instrument panel support beam are diverse and include die casting of light metals such as aluminum and magnesium and metal extrusions. Examples of instrument panel structures are disclosed in U.S. Pat. Nos. 5,564,769 and 5,934,733 for use in a vehicle having opposing side pillars, so called “A Pillars.” A complex molding of plastic material is disclosed in U.S. Pat. No. 6,520,849. In one exemplary disclosure by Pat. No. 6,520,849, there is an integrated structural HVAC system called an ISHS that includes two sections with the ISHS first section having a molded first cross beam which includes integral molded features and the ISHS second section likewise comprises a molded second cross beam having integral molded features. In the second exemplary disclosure by U.S. Pat. No. 5,564,769, there is a reinforced instrument panel assembly capable of being preassembled and then installed as a unit in a motor vehicle. Hydroforming of steel tubing is known in the art and two examples are disclosed in U.S. Pat. No. 5,353,618 a related divisional Pat. No. 5,865,054, both providing an apparatus for forming a frame member for an automobile from a tube blank by applying internal hydraulic pressure to the blank, tangent bends and preforms the internally pressurized blank into a preformed tube having a desired horizontal profile configuration, then forms the preformed tube into a finally formed frame member having a desired vertical profile configuration and a desired, varying cross-sectional configuration by placing the preformed tube in a stuffing ledge apparatus having a lower die with an upwardly facing ledge and vertically extending, punch engaging surfaces and a punch having a downwardly facing ledge and vertically extending, die engaging surfaces, internally pressurizing the tube, and then ramming the punch downwardly to form the tube into the finally formed frame member, the ledges and vertically extending surfaces substantially completely enclosing a portion of the tube before and while the punch and die come together to form the tube into the finally formed frame member. The forming components in each apparatus are submerged in an aqueous bath, allowing the blank and tube to automatically fill themselves, thereby facilitating sealing and pressurizing of the tube. Such a cross beam arrangement is believed a lightweight and less costly to fulfill the need for an instrument panel support beam. An improvement to the construction of the instrument panel support beam follows important considerations in the selection of the tubular workpiece used in the hydroforming or competing manufacturing techniques for producing an automotive instrument panel support beam as well as an automotive fuel tank filler tube. Significant considerations for selecting the configuration of the tubular workpiece include the weight of the finished beam, dimensional stability, material costs, and production costs. A need is believed to exist for the provision of a preformed tubular metal workpiece having different diameters along the length and preferably the reduced diameter section having essentially the same or reduced wall thickness for use in a subsequent hydroforming or competing manufacturing process to form the desired automotive instrument panel support beam.
It is an object of the present invention to provide a process for reducing the diameter of essentially only a select length of a tubular metal blank by the use of tension applied to pull the metal blank in a die or a succession of dies so that the reduction to the diameter of the tube is accompanied by a minimum of thickening to the wall thickness and if desired a reduction to this wall thickness.
It is still another object of the present invention to provide a two step drawing operation using contour dies to produce an elongation and a contouring of unitary tubular metal workpiece for the manufacture of an automotive instrument panel support beam.
It is another object of the present invention to provide a draw forming operation for a tubular workpiece wherein multiple drawing operations are performed with the second and any additional drawing operation being controlled to selectively impart a progressive stepped configuration of spaced apart reduced diameters spaced along the newly elongated length of only part of the tubular metal blank for the manufacture of an automotive instrument panel support beam.
The present invention seeks to minimize the wall thickness and thus also the weight of the metal tubular structure manufactured to form an automotive instrument panel support beam or an automotive fuel tank filler tube. The selected tubular metal workpiece with a uniform diameter throughout the length thereof is subject to metalworking operation selected to avoid the disadvantages arising out of the use of the rotary swaging and cold pilger processes by drawing the tubular metal blank only partly through a contoured die or a succession of contour dies. The drawing process operates to reduce the diameter of the metal tubular blank which greatly reduces increases to the tubular walls undergoing the reduction to the diameter particularly as compared to the unwanted thickness increases to the tubular walls when acted on by the rotary swaging or the cold pilger processes.